Collaborative workflows are something we've discussed adding support for in the future, but it's not a simple feature to implement.

You need some sort of permissions model to make sure that you can control which projects other folks can see/sync with; you also need a similar set of controls to grant/deny access to your account on your sync server.

Oh yeah, and then you have to start pulling items from, sending items to, and attempt to handle overlapping changes from multiple OmniFocus databases without screwing any of them up in the process. :-)

Adding your vote to the feature request we have open on this, though, so the rest of the team will know you'd like to see us support this. Thanks!